Without weed control, a farmer might make a few bushels of corn or soybeans, but a producer could make no harvestable cotton. Cotton is a tropical perennial grown in warm temperate regions as a summer annual, and is a poor competitor against many of the weeds that infest the Southern and Southwestern United States. Following planting, cotton requires 8 weeks of weed-free growth to make maximum yields. Good yields require greater than 95% weed control. Excellent yields require 99% or better control. Such, near perfect control is needed to avert difficulties with picking, excess trash in the harvested lint, and a recurring cycle of heavy weed seed fall, followed by emergence of high populations of weeds the next spring.
Before the advent of transgenic, herbicide-resistant cultivars that enabled cotton growers to use broad-spectrum herbicides, cotton weed management typically required pre-plant tillage, 3-5 herbicides applied at least 3 times during the cropping season and 2 or more cultivations. The use of broad-spectrum herbicides greatly accelerated the adoption of conservation tillage in cotton, largely eliminated in-season cultivation, reduced in-crop herbicide use, and increased the speed, flexibility, and reliability of weed management in cotton. Achievement of such improved weed management at reduced costs has prompted producers to rely heavily on a few herbicides. Rotation of tillage practices, where possible; of crops, when economically feasible; and diversification of the herbicides used are needed to conserve the efficacy of the relatively few herbicides upon which cotton weed control depends.
Confirmed, resistant populations of Palmer amaranth are found in Arkansas, Georgia, North Carolina, South Carolina, and Tennessee
provided by the Weed Science Society of America